CameraViewer.cs

using UnityEngine;

public class CameraViewer : MonoBehaviour
{

    // Update is called once per frame
    void Update()
    {
        if (Application.isMobilePlatform)
        {
            bool updateFlag = UpdateTouchParams();
            if (updateFlag)
            {
                UpdateTouchRotation();
                UpdateTouchMove();
            }
        }
        else
        {
            this.UpdateMouseRotation();
            this.UpdatePositonWithMouseScroll();
            this.UpdatePositionWithKey();
        }
    }

    #region MOBILE_TOUCH

    private int touchCntParam;
    private Touch[] previewTouches = new Touch[2];
    private Touch[] currentTouches = new Touch[2];

    private bool UpdateTouchParams()
    {
        int touchCnt = Input.touchCount;

        for (int i = 0; i < 2; ++i)
        {
            previewTouches[i] = currentTouches[i];
        }
        for (int i = 0; i < touchCnt && i < 2; ++i)
        {
            currentTouches[i] = Input.GetTouch(i);
        }

        if (touchCnt == 0) {
            touchCntParam = 0;
            return false;
        }
        if(touchCntParam >= 0 && touchCntParam < touchCnt)
        {
            touchCntParam = touchCnt;
            return false;
        }
        if(touchCntParam > touchCnt)
        {
            touchCntParam = - 1;
            return false;
        }
        return true;
    }
    private void UpdateTouchRotation()
    {
        if (Input.touchCount != 1 || touchCntParam != 1)
        {
            return;
        }
        var delta = this.currentTouches[0].position - this.previewTouches[0].position;


        delta = (delta / Screen.dpi) * 80.0f;

        AddCameraAngle(delta.x, -delta.y);
    }
    private void UpdateTouchMove()
    {
        if (Input.touchCount != 2 || touchCntParam != 2)
        {
            return;
        }
        float prevDist, currentDist;
        Vector2 prevCenter, currentCenter;

        CalcDoubleTouchParam(currentTouches[0], currentTouches[1], out currentDist, out currentCenter);
        CalcDoubleTouchParam(previewTouches[0], previewTouches[1], out prevDist, out prevCenter);

        Vector3 move = new Vector3(currentCenter.x - prevCenter.x,
            currentCenter.y - prevCenter.y,
            currentDist - prevDist);

        move = (move / Screen.dpi) * 10.0f;

        move = transform.rotation * move;
        transform.position += move;
    }

    private void CalcDoubleTouchParam(Touch t1,Touch t2,out float distance,out Vector2 center)
    {
        distance = (t1.position - t2.position).magnitude;
        center = (t1.position + t2.position) * 0.5f;
    }
    #endregion MOBILE_TOUCH

    #region KEY_AND_MOUSE
    private void UpdatePositonWithMouseScroll()
    {
        float wheel = Input.GetAxis("Mouse ScrollWheel");
        var move = transform.forward * wheel * 3.0f;
        this.transform.position += move;
    }

    private void UpdatePositionWithKey()
    {
        var move = Vector3.zero;
        if (Input.GetKey(KeyCode.W) || Input.GetKey(KeyCode.UpArrow))
        {
            move += transform.forward;
        }
        if (Input.GetKey(KeyCode.S) || Input.GetKey(KeyCode.DownArrow))
        {
            move += -transform.forward;
        }
        if (Input.GetKey(KeyCode.D) || Input.GetKey(KeyCode.RightArrow))
        {
            move += transform.right;
        }
        if (Input.GetKey(KeyCode.A) || Input.GetKey(KeyCode.LeftArrow))
        {
            move += -transform.right;
        }
        if (Input.GetKey(KeyCode.Space))
        {
            move += transform.up;
        }
        if (Input.GetKey(KeyCode.LeftShift))
        {
            move -= transform.up;
        }
        transform.position += move * Time.deltaTime * 10.0f;

    }

    private void UpdateMouseRotation() { 
        if ( Input.GetMouseButtonDown(0))
        {
            Cursor.lockState = CursorLockMode.Locked;
        }
        else if (Input.GetMouseButton(0))
        {
            this.AddCameraAngle((Input.GetAxis("Mouse X") * 3.0f), (Input.GetAxis("Mouse Y") * -3.0f));
        }
        if (Input.GetMouseButtonUp(0))
        {
            Cursor.lockState = CursorLockMode.None;
        }
    }
    # endregion KEY_AND_MOUSE

    private void AddCameraAngle(float dx , float dy)
    {

        var rotation = this.transform.rotation;
        var angles = rotation.eulerAngles;
        angles.y += dx; 
        angles.x += dy; 
        if (angles.x > 180.0f)
        {
            angles.x = angles.x - 360.0f;
        }
        angles.x = Mathf.Clamp(angles.x, -85.0f, 85.0f);
        rotation.eulerAngles = angles;
        transform.rotation = rotation;
    }
}